This invention relates to a system for measuring the radiation power of power-modulated transmitters, in particular of lasers, including an opto-acoustical converter converting the radiation modulation into gas-pressure modulation.
When operating with power intense radiation sources, in particular with lasers, a monitoring of the radiation power is required for measurement reasons and in view of protection regulations. This power control is at present effected in such a way that permanently or temporarily at least a part of the radiation is supplied to a detector which completely absorbs the radiation. The conventional methods mostly cause an interfering access to the radiation path and require labor for adjusting the radiation of the detector. An alteration of the adjustment may indicate an actually not existing variation of the radiation power during measurement.
A detector known for such radiation power measurements, in particular in the infra-red range, is the Golay cell operating on the opto-acoustical principle. It comprises a gas-filled space which has a window for the passage of the modulated radiation to be measured and opposite to the window a black surface completely absorbing the radiation. The space is secluded by a diaphragm deflectible by pressure fluctuations of the gas, the deflections of which diaphragm are measured, e.g. by means of a mirror arrangement. By absorption of the radiation at the black surface, the gas is heated with the frequency of the radiation modulation. The pulsations of the gas pressure caused thereby are proportional to the radiation power in their amplitudes and may therefore serve as a measure therefor. In other measuring systems based on the opto-acoustical effect, microphones have also been employed for the measurement of gas pressure fluctuations.